(517a) Production of Inherently Separated Syngas Streams Via Chemical Looping

 Production of Inherently
Separated Syngas Streams via Chemical Looping

Amey More and
Götz
Veser

 Department
of Chemical Engineering, University of Pittsburgh, Pittsburgh, PA

Abstract:

?Chemical Looping Combustion' (CLC) is an
emerging clean combustion technology which offers an efficient and elegant
route for fossil fuel combustion with inherent CO₂ capture based on
the cyclic oxidation and reduction of an ?oxygen carrier? (typically a metal)
with air and a fuel, respectively. However, chemical looping can be used for
fuel conversion well beyond combustion. We have previously shown that chemical
looping allows for highly efficient production of synthesis gas from methane
via partial oxidation. In the present work, we propose the formation of
separated streams of CO and high-purity H₂ via non-oxidative methane
cracking and oxidative removal of the produced carbon using CO₂ in a
?looping configuration?, i.e. at periodic process conditions.  The proposed
process utilizes the well-known reactivity of Ni towards C-H bond activation
(which also makes Ni/NiO a popular oxygen carrier for conventional chemical
looping combustion). CH₄ is cracked catalytically over Ni, producing
gaseous H₂ and solid carbon which deactivates the carrier. The
carrier is then regenerated by burning off the carbon using CO₂ as
oxidizer_, enabling the reduction of CO₂ to CO.

Supported Ni carriers were synthesized
using a simple wet-impregnation procedure and characterized using X-Ray
Diffraction (XRD) and Electron Microscopy (SEM, TEM, EDX). Solid state and gas
phase conversions and selectivities were determined via thermo-gravimetric
analysis (TGA) combined with fixed bed reactor studies. We found that the nature
of the support strongly influences particle size and distribution of the active
metal species (Ni) and thus impacts the overall activity of the carrier towards
methane cracking. Furthermore, these differences also impact the morphology of
the carbon formed during the cracking reaction, which further impact overall
carrier reactivity. Similarly, the oxidative removal of the carbon by CO₂
depends strongly on the type of carbon formed and hence on support properties. Based
on these observations, suitable process conditions were identified and a simple,
yet promising carrier system for an efficient chemical looping process for the
production of separated syngas streams (i.e. separate H₂ and CO effluent
streams) is proposed.